In the datura plant, purple flower color is controlled by a dominant allele P. White flowers are found in plants homozygous for the recessive allele p. Suppose that a purple-flowered datura plant with an unknown genotype is self-fertilized and that its progeny are 28 purple-flowered plants and 10 white-flowered plants.

Part A

Use the results of the self-fertilization to determine the genotype of the original purple-flowered plant.

a. Pp
b. PP
c. pp

Part B

If one of the purple-flowered progeny plants is selected at random and self-fertilized, what is the probability it will breed true?

a. 1/3
b. 1/4
c. 3/4
d. 2/3

A: The purple flower color is regulated by dominant allele "P". Since self-fertilization of the purple-flowered plant with unknown genotype gives both purple and white-flowered progeny in almost 3:1 ratio, the parent plant was heterozygous dominant for the trait. Its genotype is "Pp".

Segregation of recessive and dominant alleles during gamete formation leads to the production of two types of gametes with either "P" or "p" alleles. The random fusion of these gametes produces progeny in following phenotype ratio= 3 purple: 1 white.

B. Out of the 3 purple-flowered progeny, 1 is homozygous dominant (PP). Therefore, the probability of the purple-flowered progeny to breed true is 1/3.